Recently, research on side-chain liquid crystals which has applicability for photo-electric devices is being widely progressed. Most of the side-chain liquid crystals are limited to the compounds such as siloxane derivatives, acrylate derivatives, methacrylate derivatives, etc., all of which are known to have no conductivity.
Moreover, the vast majority of conventional conducting polymer is insoluble in organic solvents and their oxidation stability with respect to the air and thermal properties are not good. Especially, processability is not good. In the case of using conducting monomers such as thiophene, pyrrole, paraphenylene, etc., conducting polymers insoluble in organic solvents were prepared owing to a problem with the synthetic method therefor. Recently, by incoporating a thiophene derivative having a great number of carbon atoms at the 3-position of the thiophene, a conducting polymer soluble in organic solvents was prepared.
However, this kind of organic solvent-soluble conducting monomer is somewhat difficult to synthesize. Also, electric polymerization should be applied (see J. R. Reynolds, Macromolecules, 1991, Vol. 24, p678; and Japanese Patent Laid-open Publication No. hei 3-086721).
Meanwhile, a side-chain liquid crystal polymer is a material having high applicability as a membrane which can control the permeation of pharmaceuticals or gas. The membrane can selectively permeate special properties and/or materials to the flow of heat or material. A method for the separation of gases using the membrane is proceeded using the difference of the permeation velocity of each of mixed gases to pass through the semi-permeable membrane.
Recently, research has been actively concentrated on a membrane separation process among various separation processes and particularly on a process for an oxygen enrichment membrane. The oxygen-enriched air is used for a combustion system or in the medical field, while nitrogen-enriched air is industrially used for cleaning ambient air in connection with semiconductor manufacturing facilities.
Requirements for the oxygen enrichment membrane are as follows.
1. high permeability for oxygen (high P.sub.O2)
2. high separability for oxygen (high P.sub.O2 /P.sub.N2)
3. thermodynamic stability and durability
The permeability of the gases for a non-porous polymer membrane depends on the phase of the polymer, i.e., whether rubber phase or glass phase. The polymer of the rubber phase shows fast reaction on the gases dissolved in the membrane, as a result of the flexible backbone. However, the problem of the difficulty in formation of a thin film exists.
A polymer which is capable of manufacture into a thin film using an organic solvent and has high gas permeability can be manufactured by employing a rigid backbone and a flexible side chain poly(dimethylsiloxane) (PMDS) or poly (1-(trimethylsilyl)-1-propyne), which is used as an oxygen enrichment membrane among the known polymers, shows high permeability. However, drawbacks such as low selectivity or difficulty in manufacturing remain.
The inventor of the present invention has performed research on preparing a novel conducting polymeric side-chain liquid crystal by incoporating liquid crystalline compounds in a conducting monomer such as a diacetylene derivative, thiophene derivative, pyrrole derivative, aniline derivative, etc., using various synthetic methods, to carry out a study on the relation between conductivity and liquid crystallinity.